In recent years it has been found that one class of active herbicides are the substituted phenylpyrazoles, the phenyl and pyrazole moieties of which contain a variety of substituents.
Methods of manufacturing these phenylpyrazoles commonly involve chemical conversions of one or more radicals substituted on the phenyl and/or pyrazole moieties, e.g., by halogenation, esterification, etc. It is also known to prepare these compounds from substituted acetophenones by interaction with various compounds, including various esters which contribute the desired substituent radical to the 5-position of the pyrazole radical via cyclization of an intermediate phenyl diketone. For example, various halo- and/or alkyl-substituted acetophenones have been reacted with (halo) acetic acid esters to produce the corresponding phenyl diketone which is cyclized with hydrazine to yield phenylpyrazoles substituted in the 5-position of the pyrazole radical with (halo) alkyl groups.
It has recently been disclosed that certain 3-substituted aryl-5-substituted pyrazoies are particularly useful for broadspectrum control of a variety of weeds at very low application rates in a number of agronomically important crops. The aryl group is typically the phenyl radical substituted with halogen, alkyl, alkoxy and ester groups, substituents which are also commonly found on the pyrazole moiety. Particularly effective within this class of compounds are esters of 2-chloro-5-(4-halo-1-methyl-5-(trifluoromethyl)-1H-pyrazol-3-yl)-4-fluorob enzoic acid. These particular compounds are most readily available from 2-fluoro-5-alkylacetophenones and their derivatives. The literature, however, does not provide methods of preparation of these intermediates or related compounds that could provide the desired pyrazolylbenzoic acid esters. Thus, there is a need in the art for the discovery of novel intermediates and for efficient methods for the preparation of these substituted arylpyrazole compounds.
The present invention describes intermediates useful for production of compounds within this new class of herbicides.